| The total volume of annual water supply of the City of Beijing is 40-42×108m3 presently. Of which, 26-28×108m3 is from groundwater sources, accounting for over 2/3 of the total . Owing to the successive drought and consequently long-term over-exploitation of groundwater, the city is suffering from a serious water crisis. At the end of November in 2003, the water storage in Miyun Reservoir and Guanting Reservoir has reduced to only 7.6×108m3 and 2.1×108m3 respectively, which are the two most important surface water supply sources for Beijing. As a result of the insufficient surface water resources, groundwater was exploited in very big amount in 1999 to 2003, which was a 5-year dry period. On the other hand, the recharge of groundwater was only 16-18×108m3 in the period from 1999 to 2003, which only accounts for less than 2/3 of the average amount. The water supply shortage is solved from reservoir storage and groundwater. Consequently, the groundwater storage in the plain area in Beijing reduced drastically by an amount of 57.45×108m3 from 1980 to 2002. All kinds of environment geological problems stood out more and more because of excessive exploitation.The groundwater investigation and resources assessment have been carried out for several times for the City of Beijing during the past years. And the results from most of the assessments indicate that the exploitable groundwater resources are 26.33×108m3 for the city, of which 24.55×108m3 for the plain area. However, these assessment results are not able to reflect the difference of annual groundwater recharge in years with different precipitation, especially the recharge in very dry years, to reflect the changes on the aspect of groundwater development and utilization, to reflect the features of the groundwater recharge, discharge and storage changes in different years.It doesn't reflect the actually situation to use the result of multi-year average assessment. On the planning of water resources, groundwater resources assessment result that was obtained on the basis of multi-year average is often used for long-term planning. But it is not proper to use this result for short to medium term planning, especially when a long drought period, such as the 5-year in 1999-2003 in Beijing, occurs. When emergent exploitation of groundwater has to be done, the capacity of the groundwater system to sustain this kind of extreme action should be studied, considering a number of constraints.In this paper, the volume of groundwater storage, excharge, discharge and the volume of storage change were analysed according to studying in-depth about water resources. The main conclusions like these:It is calculated that the total groundwater storage of the quaternary aquifers in the plain area in Beijing is 1117.29×108m3, of which 619.14×108m3 is for the aquifer within 150m below the surface. This large amount ensures that there is enough water stored in the aquifer for emergent exploitation.The volumes of groundwater charge in different period and different probability were studied in methods of statistics and hydro-analysing in Beijing Plain.The average annual recharge of the quaternary groundwater system in the plain area of Beijing was calculated as 27.38×108m3 for the period of 1980-2002, which is 3.37×108m3 less than that for 1961-1980. It is also found that the difference of the recharge in different years has become more significant since 1980: the recharge was 27.39×108m3,23.17×108m3 and 17.06×108m3 when the probability is 50%, 75% and 95% respectively.The index of groundwater exploitation degree was difined and it is the key to weigh the reasonability of groundwater exploitation and assessment. Moreover, the coefficient of the exploitable amount of groundwater was caculated from the index. After 1980, the amount of groundwater exploitation was averagely 25.77×108m3. The index of groundwater development is 0.80 to 0.94, and the average is 0.90. This indicates that the groundwater system has been over-exploited and the natural discharge has b...
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